System for supervision and control of objects or persons

ABSTRACT

A system for supervision and control of objects or persons within a limited area, such as a building, comprising a plurality of electronic identification chips for placing on respective objects/persons to be supervised/controlled, each chip having stored therein a special ID code and being provided with respective transmitters and receivers for communication via ultrasound as well as audible sound, a plurality of stationary detectors which are interconnected in a network and arranged for both-way communication with the chips, and a central control unit in communication with the chips via the detectors. Each chip is continuously active in operation and is arranged to transmit its ID code at predetermined time intervals. At least one of the detectors or the control unit are being arranged to trigger an alarm unit if an incorrect code is received or an approved code is not received continuously at predetermined time intervals.

The invention relates to a system for supervision and control of objectsor persons within a limited area, such as a building, comprising aplurality of electronic identification chips for placing on respectiveobjects/persons to be supervised/controlled, each chip having stored aspecial ID code and being provided with a transmitter and a receiver forcommunication via ultrasound, a plurality of stationary detectorsinterconnected in a network and arranged for both-way communication withthe chips, and a central control unit communicating with the chips viathe detectors.

There is previously known a system of the above-mentioned type which isconstructed for localizing persons by means of individual badges ormarker chips, and wherein the system is based on signalling by means ofultrasound. In this known system the badges have an ultrasonic signaturewhich is extractable by means of special ultrasonic sensors mounted inwalls or ceilings in e.g. a building, and wherein the sensors constitutea transceiver which is able to transmit and receive an ultrasonic signalover a distance range of up to 10 m. The system comprises a control unitcommunicating with the badges via said sensors. When a badge is situatedin the communication region of a sensor, the control unit stores theidentification number of the badge, the identification of the sensorencountering the badge, and date and time for the coincidence. Thisinformation is transmitted in coded form by means of ultrasound to acentral control unit in the form of e.g. a computer or PC.

A substantial weakness of the previously known system is that signallingwith ultrasound is dependent on a free visibility between the markedobject and the current sensor or detector, or a high degree ofsaturation of the localization area with ultrasound from a large numberof transmitters. In order to remedy this weakness, some systems haveadded signalling by means of radio signals. However, this createsproblems for electronically sensitive equipment.

The above-mentioned known system neither can be used in anotherimportant field of application, viz. with active supervision and controlof objects, persons etc. within a complex of buildings, a building orparts of a building. Such supervision and control is of substantialimportance within many fields of the society. As examples there may bementioned hospitals and other health institutions, insurance companies,factories, laboratories, air ports, banks, military installations, guardcompanies, hotels, offices, shops, dwellings, etc.

A problem or a weakness with the known systems for access and movementcontrol, is that they are switched off when authorized personnel iswithin the supervised or controlled area. This implies that also otherpersons can get into and/or move freely within the same area without analarm being triggered. Thus, within the same system, there is notdistinguished between access control and the number of persons that canmove (authorized or non-authorized movements) after having passed theaccess control. This means reduced security and reduced survey/control.The same otherwise applies to private dwellings where unauthorizedpersons seek entry with the intention of profit while persons arepresent, because a possible alarm then is switched off.

Another weakness of the existing systems is the lacking safety ofauthorized personnel. As a consequence of the fact that the alarms inmost cases are switched off after adequate admission through coded,electronic or other control systems, unauthorized persons can—when thealarm is switched off—easily move within such areas if they haveobtained access to forbidden zones. Dangerous situations and unsafeworking places thereby arise, especially in the evening and at night.There are many examples of personnel in such situations having beenassaulted by thieves or drug addicts in desperate pursuit of narcotics,cf. hospitals. Especially, existing systems manage badly in largeinstitutions having a large personnel traffic, such as applies tohospitals, military quarters, banks, etc. Especially the unsafety of thepersonnel increases from daytime to afternoon, evening and night.

An additional weakness or drawback of the existing systems is that theyonly to a small extent allow differentiation of the alarm generation inthe effected access/movement control. For example, traffic in a hospitalcorridor or a transport conduit will be able to give alarm with anymovement, or no alarm at all when access authorization has beenobtained.

In active supervision and control of objects it is often also importantto be able to provide for routine maintenance of equipment which has tobe taken in for control and testing after given time periods. In somecases it is also the total operating time of the equipment which is thecriterion for calling in for control and testing.

There exist data systems with software which takes care of routinemaintenance of said type. The location of the equipment of interest thenis generally recorded in a central computer. The drawback of these knownsystems is that they do not automatically manage to locate equipmentwhich is moved, and that they therefore require use of time andresources from personnel to recover such mobile equipment or tools.Equipment which is only to be used a given number of operating hours,will also require much resource use and severe demands on human routinesin that personnel physically must check and keep control over theoperating time. Common to the known systems is that they are based on agreat administrative work with the effort of considerable labour,careful and accurate registrations of equipment and operating time, andrunning maintenance programs. These operations have in common that agreat discipline from many people is required, something which oftenfails and involves a need for a great effort of labour. Seeking isperceived as unnecessary trouble and delay, and therefore results. in apoorer working environment and a great turnover of personnel.

On this background it is an object of the invention to provide aflexible and programmable system which provides for access and movementcontrol of persons, objects and documents within a complex of buildings,a building or parts of a building, at the same time as theabove-mentioned weaknesses/drawbacks are avoided, so that authorizedpersonnel can move freely within the topical area while an alarm will begiven if unauthorized persons get into the same area.

The above-mentioned object is achieved with a system of theintroductorily stated type which, according to the invention, ischaracterized in that each chip and each detector also is provided witha transmitter and a receiver for communication via audible sound(audio), a means being provided for switching between ultrasonic andaudio communication, and that each chip in operation is continuouslyactive and is arranged to transmit its ID code at predetermined timeintervals, the detector or the control unit being arranged to trigger analarm unit if an incorrect code is received or an approved code is notreceived continuously at chosen time intervals.

In the system according to the invention authorized personnel isequipped with an active ID chip with both-way wireless ultrasonic andaudio communication and having a special ID code for the person carryingthe chip. In case of entry into an area requiring authorization, thesystem will recognize the chip and fail to give an alarm. This takesplace in that the chip at a preprogrammed time interval gives a codedmessage to detectors placed around in relevant areas that it is presentand is authorized. The detectors, which may either be a separateself-contained unit or a subcomponent in a superior central system, willverify the ID code emitted by the chip. Chips emitting codes which arenot in accordance with allowed codes, will cause activation of the alarmsystem, locally or centrally. This takes place in that a number ofstationary detectors, which are interconnected in a network and arearranged for both-way communication with the chips, and a main centralor subcentral communicating with the chips via the sensors/detectors andpossible repeaters, will activate the alarm system. Similarly,unauthorized persons without such chips will do the same in that theyenter into zones covered by detectors. These detectors are constructedfor reacting both to ultrasonic and audio signalling and also tomovement within their area. The principle of detection of movement maybe both infrared radiation (IR) and ultrasound, or other knownprinciples.

A further object of the invention is to provide a system providing forcalling and localization of objects and equipment, for example inconnection with automatic call-in to routine or operational maintenanceof equipment which must be brought in for control and testing aftergiven time periods.

This object is achieved with a system of the introductorily stated typewhich, according to the invention, is characterized in that each chipand each detector also is provided with a transmitter and a receiver forcommunication via audible sound (audio), a means being provided forswitching between ultrasonic and audio communication, and that thecentral control unit is arranged to selectively call a chosen chip viathe detectors, and that the chips are arranged to give an answer as areaction to the call, the closest situated detector then identifying thesite/locality of the chip.

In the above stated system the central control unit will, in case of arequirement for routine maintenance of equipment, automatically give amessage to the detectors which in turn will call the relevant marker orID chip. The chip will respond, and the detector which is closest, willgive a message, and since a detector is stationary, the location isdefined within the communication distance between the chip and thedetector. The chips also have the possibility to activate themselvesafter a preprogrammed time interval. If some equipment has a requirementfor test and control after a certain number of hours of operation, thechip may contain inputs registering the length of active operating timehaving elapsed at any time, and give a return message to the centralcontrol unit. The advantage which is achieved, is that one has anautomatic system which does not need to pay regard to human routines inthat personnel physically must check and keep control over the operatingtime and the errors which may normally arise in this connection.Further, the system is very resource-saving in that all the time one hascontrol from a central location of where equipment is located, and thenespecially portable/movable equipment.

A substantial advantage of the system according to the invention is thatit does not “contaminate” the environment within the range ofapplication of the system with electromagnetic fields which may disturbelectromagnetically sensitive equipment. This is of substantialimportance, for example in a hospital environment.

A field of application wherein the system according to the inventionwill be very advantageous, is in retrieval of journals (patientjournals) and equipment in hospitals. In this connection the combinationof sound and ultrasound will increase the detection from about 60% whenusing only ultrasound to 100% with sound. The combination is bothimportant and advantageous, as audio communication is introduced onlywhen one does not find “the target object” with detection of ultrasoundalone. Thereby on avoids “contamination” of the environment to a toogreat extent. Possibly one may also use audio communication in anupdating of the location of all the topical objects (patient journals)at certain times of the day, for example evening and/or morning.

Thus, the system provides a safe retrieval of journals and equipment,provided the relevant rooms have got a detector installed. This meansthat it is not necessary to have free lines of sight to the objects ofinterest, or to saturate large areas with ultrasound by means of manywave generators. Ultrasound is easily stopped by physical obstacles,such as paper. Safe detection therefore would require a system whichcould also pick up ultrasonic waves reflected from walls, objects, etc.,something which is technically difficult and would result in a moreexpensive solution. This is the reason why the problem with retrieval ofjournals and equipment in confined rooms has not previously been solvedin a satisfactory manner. As mentioned above, some systems have added RFcommunication. However, the limitation to rooms then will not besufficiently accurate without the help of large number of aerials, andat the same time one gets undesired electromagnetic fields.

The system according to the invention also provides automatedmaintenance routines with indication of the place where the equipment islocated, something which gives large possibilities for rationalizationprofits in relation to the systems of today, especially when it is thequestion of portable or movable equipment.

The invention will be further described below in connection withexemplary embodiments with reference to the drawings, wherein

FIG. 1 shows a survey view of a system according to the invention,installed in a number of rooms in a supervised area of a building;

FIG. 2 is a block diagram showing the main elements in the systemaccording to the invention;

FIG. 3 shows an example of the construction of an ID chip in the systemaccording to the invention;

FIG. 4 shows an example of the construction of a room detector in thesystem according to the invention;

FIG. 5 shows a schematic perspective view of an embodiment of anelectroacoustic transducer used in the transmitters and receivers of achip;

FIG. 6 shows a schematic cross-section of another embodiment of anelectroacoustic transducer which may be used in the receivers;

FIG. 7 is a flowchart showing operating steps carried out in a chip;

FIG. 8 shows a flowchart corresponding to that of FIG. 7, for a chipwhich is provided with inputs and outputs for operational data from anobject on which the chip is mounted; and

FIG. 9 is a flowchart showing operating steps carried out in a roomdetector.

In FIG. 1. a floor area 1 of a building is shown to be divided intoeight rooms RM1-RM8, and a passage or corridor CR arranged between therooms. In the rooms and in the corridor there are mounted a number ofdetectors DT1-DT10, more specifically two detectors in a room RM1 andone detector in each of the remaining rooms RM2-RM8 and in the corridorCR. Further, marker or ID chips are situated in some of the rooms, morespecifically respective chips ID1-ID5 in the rooms RM2, RM7, RM8, RM5and RM3. All the detectors are connected to a network 2 which, in theillustrated example, is in connection with a pair of central controlunits, more specifically a subcentral 3 and a main central 4. In thenetwork there is also shown to be connected a repeater 5, i.e. a unitfor amplifying the signals in the network. Further, the centrals are inconnection with alarm units 6.

The fundamental construction of the total system appears from FIG. 2.The figure shows a central control unit or central unit 10 which,through a network 11, is in both-way communication with a plurality ofdetectors, here represented by a room detector 12. Each of the detectorsis in wireless, both-way communication with the marker chips (!ID chips)of the system. The information is transmitted by frequency modulation.The connection in the figure is designated by 13, whereas the chips arerepresented by a chip 14. The network 11 connecting the room detectors12 with the central unit 10, may be of different character. There may beused a separate line system in the form of a two-wire parallelinterconnection or star-type network, an existing line system forinternal telephone or alarm installation, mains or data network.Different techniques are used for adaptation to the different networksolutions.

As mentioned, the signalling between the chips and the room detectorstakes place by means of ultrasound or audible sound (audio). As known,the ultrasonic signals have the property that they do not easilypenetrate walls and ceilings, as is the case with high-frequency radiowaves. This makes it possible to determine the location of the markerchips to concrete rooms or parts of large rooms. The range of ultrasonicsignals is of the order of 10-15 m. Larger rooms therefore must haveseveral is detectors.

Essential features of the three main elements of the system, i.e. thechip 14, the room detector 12 and the central unit 10, may be summarizedas follows:

The chip 14 is a miniature electronic unit which, by means of ultrasoundor sound, can transmit and receive signals within a room. The chips haveindividual identification codes. The chips may have inputs and outputsin order to be able to check the condition (e.g. the operating time) ofobjects to which they are fastened.

The room detector 12 is a unit which, by means of ultrasound or sound,can transmit and receive signals to and from chips in the same room. Theroom detector can transmit and receive signals to and from the centralunit and/or from a possible subcentral. In addition, the room detectorcan have other types of sensors or detectors for detecting movement orother incidents in the room.

The central unit 10 communicates with all the detectors via a networkwhere also subcentrals may be arranged. The central unit receivesinformation from chips and from room detectors. The central unitprocesses received information from chips and prestored informationrelating to the authorization of the chips, and generates alarms andwarnings according to predetermined criteria.

As shown in FIG. 2, the central unit 10 may consist of a PC equippedwith software which is especially developed for the purpose and is veryflexible with respect to adaptation of functions in the system to thedifferent fields of application.

An example of the construction of a marker chip or ID chip 14 is shownin FIG. 3. The chip comprises a control circuit in the form of amicrocontroller (μC) 20 controlling the different operations of thechip. Power supply to the μC circuit 20 and to the remaining circuits ofthe chip is provided from a battery 21. The chip communicates with theroom detectors 12 via an ultrasonic transmitter (US transmitter) 22 andan ultrasonic receiver (US receiver) 23. Digital signals from the μCcircuit 20 is supplied to the US transmitter 22 via a signalconditioning circuit (D/A converter) 24 and an amplifier 25, whereasanalogue signals from the US receiver 23 is supplied to the μC circuitvia an amplifier 26 and a signal conditioning circuit (A/D converter)27. The chip 14 further communicates with the room detector 12 via asonic or audio transmitter (AUD transmitter) 28 and a sonic or audioreceiver (AUD receiver) 29. Digital signals from the μC circuit 20 aresupplied to the audio transmitter 28 via a signal conditioning circuit30 and an amplifier 31, whereas analogue signals from the audio receiver29 are supplied to the μC circuit via an amplifier 32 and a signalconditioning circuit 33.

The chip 14 further contains a signal switching circuit 34 for switchingbetween ultrasonic and audio signalling, and which is in the form of aswitch or selector (time multiplexer) controlled by the μC circuit 20,so that the selector 34 provides for switching between audio andultrasound at chosen time intervals. This change-over or switching willbe further described below.

The microcontroller 20 of the chip operates as a state machine havingseveral states, wherein it alternates between listening to theultrasonic receiver 23 for a short time (100-200 ms) within a timeinterval of ½ second, and to the audio receiver 29 for a similar shorttime within an interval of ½ second. The microcontroller controls thealternation by means of a built-in timer and the selector 34. The timergives time-out after ½ second, and switches the selector. If the chipreceives a valid signal while it is in the listening states, and this isa valid message, and the message ask for the identity of the chip, thestate machine of the μC circuit will pass on to the transmitting mode.The chip then will transmit in the same frequency band as the received,valid ultrasonic or audio message, and respond with a predefined messageto the detector 12. Immediately after the response has been delivered,the μC circuit 20 passes from the transmitting state back to thelistening state according to the same alternating pattern as thatdescribed above.

The chip normally is in the listening mode, and only passes on to thetransmitting mode when there is transmitted. The chip immediately goesback to the listening mode. If it is the question of a chip havinginputs from external equipment (see below) or a chip which for somereason is to transmit information uninvitedly to the detector, the statemachine of the μC circuit will pass from the listening state to thetransmitting state, and the signal selector 34 will choose theultrasonic transmitter 28 as the source. The μC circuit 20 will transmitinformation via ultrasound, and thereafter will change state to thelistening mode. At the same time a built-in timer in the μC circuit willstart, and measure the time from transmission until a response isreceived from the detector. If the transmission is answered from thedetector in the form of an ultrasonic acknowledgement message forreceived message, the timer stops and the chip remains in the listeningmode. If no such acknowledgement message comes from the detector, thechip will transmit the message anew a predetermined number of times, andif this does not result in a response message from the detector, themicrocontroller of the chip will change state to transmit (and receive)on the audible frequency band. This takes place in that themicrocontroller switches the signal selector 34 to activate the audiotransmitter 28 and the audio receiver 29. Immediately aftertransmission, the chip goes to the listening state, and if the chipreceives an acknowledgement for the message, the state machine will goback to the listening state.

The microcontroller 20 contains a memory (EEPROM) which is arranged forremote programming, addressing and processing. The memory can store thecurrent desirable data, e.g. also histories as to where the object towhich the chip is fastened, has been in a certain time period. Thememory also contains the special, preprogrammed identification code ofthe chip. The chip is arranged for automatic activation at predeterminedtime intervals, and for then to transmit a message comprising thespecial identification code. The activation can take place directly fromthe chip by means of the control circuit 20, or from the central controlunit (PC) 10 after a time period programmed in advance. The chip alsocan be arranged for automatic activation when the battery 21 is to bechanged. This ensures that the chips in the system always havesufficient current supply for correct function.

The chips suitably may be preprogrammed from a local or central computerwhile they are out in the system. This may be desirable if one wants tochange the time period in which a supervised object is out in thesystem. Thereby much time can be saved in that one is let off taking inobjects manually for reprogramming.

As shown in FIG. 3, the chip 14 possibly may be provided with a signaltransmitter 35, such as a buzzer, which is arranged to deliver a signalin case of an alarm which has been triggered by a neighbouring detector.This may represent an advantageous safety measure, since an authorizedperson, carrying the chip with the signal transmitter, then will get anindication that an unauthorized person, which may be an intruder or aburglar, is in the same security zone.

Further, as shown in FIG. 3, some chips may be provided with aninput/output unit (I/O unit) 36 having ports for reception and deliveryof information concerning service life or active operating time ofrespective objects or apparatuses on which the chips are mounted.

An example of the construction of a room detector 12 is shown in FIG. 4.In a similar manner as the chips 14, each of the detectors comprises acontrol circuit in the form of a microcontroller (μC) 40 controlling thedifferent operations of the detector, and which contains a memory(EEPROM) for remote programming, addressing and processing. The controlcircuit 40 communicates with the network 11 via an interface or modem 41which is adapted to the chosen network technology. As mentioned above,the network 11 may be 1) a separate network which is especially adaptedto the system, 2) a network for an existing alarm or callinginstallation, 3) the mains (110/220/380 V), or 4) a PC network. Forcommunication with the chips 14, the control circuit 40 further is inconnection with an ultrasonic transmitter (US transmitter) 42 via asignal adapter (D/A converter) 43 and an amplifier 44, and in connectionwith an ultrasonic receiver (US receiver) 45 via a signal adapter (A/Dconverter) 46 and an amplifier 47. The detector 12 further communicateswith the chips 14 via an audio transmitter (AUD transmitter) 48 and anaudio receiver (AUD receiver) 49. Digital signals from the μC circuit 40are supplied to the audio transmitter 48 via a signal conditioningcircuit 50 and an amplifier 51, whereas analogue signals from the audioreceiver 49 are supplied to the μC circuit via an amplifier 52 and asignal conditioning circuit 53.

In a similar manner as the chips 14, the detector 12 contains a signalswitching circuit 54 in the form of a selector controlled by the μCcircuit 40, so that the selector 54 provides for switching between audioand ultrasonic communication at chosen time intervals. This switchingwill be further described below.

During normal retrieval, the central unit 10 controls the calling of achip 14. This takes place in that the central unit sends a message tothe detector 12 about the frequency on which there is to be signalled,together with the identity of the chip which is sought. The detectorreceiving the message then will process the message, and the μC circuit40 chooses. signalling medium in the signal selector 54. This takesplace in that a state machine enters the initial stage, and the messagealways will be firstly sent ultrasonically. The beginning of the messagewill be without data, but is a continuous awakening signal to the chip.After this the message follows. When the message has been sent, thedetector will pass on to the listening mode and wait for a response froma chip. The response is expected from the chip in the same frequencyrange as that of the transmitted signal. If the detector does notreceive a response after a period of one second, a built-in timer in themicrocontroller will give time-out, and send a message about this backto the central unit. The central unit may choose to try transmission anumber of repeated times by sending the same message to the detector thesame number of times, or to send a new message where the detector iscommanded to signal on audible frequencies. This takes place in that thestate machine in the detector changes state to send via audio,whereafter the signal selector 40 is switched to activate the audiotransmitter 48 and the audio receiver 49. The same time-out protocol asfor ultrasound applies also here.

The room detector 12 further comprises a detecting sensor 55 which isconnected to the control circuit 40 via an amplifier 56 and a signalconditioning circuit (A/D converter) 57. The sensor 55 is arranged todetect movements or rather incidents in the room, and is based oncommonly known technology (ultrasound, infrared radiation, etc.).

As a result of the fact that the detectors 12 are addressable, andfurther contain both a transmitter and a receiver and are connected in anetwork, the rooms in which the current persons/objects (with ID ormarker chips) are situated, can easily be identified by means of a localor central computer.

The central unit 10 comprises a processor containing a data base withinformation about all the chips in the system. The following informationabout the chips will be entered into the data base:

function (mode),

identification,

authorized mode,

non-authorized mode,

description (e.g. name of person or type or number of an instrument,e.g. an infusion pump or a medical journal in a hospital),

different alarm levels to be activated in case of violation ofauthorization.

The main functions of the central unit may be summed up in 1)controlling functions, 2) listening functions and 3) checking functions.These main functions essentially comprise the following operations:

The controlling functions of the central unit:

Controlling the room detectors to set themselves in different modesadapted to the requirement where the detector is placed.

Transmit a general call via room detectors to chips that are to befound.

Automatically transmit a call to object marker chips to be checkedwhether they are present where they are to be.

Transmit information to definite chips about the mode in which they areto place themselves (different fields of use).

Transmit information to chips about a change of identification code ifthis is desirable (safety measure and administrative maintenance).

The listening functions of the central unit:

Receive messages from room detectors which have received a response ordata from ID or marker chips.

Receive messages from room detectors which have detected persons thatare present in a definite zone.

Receive acknowledgements of commands which have been sent out.

Receive signals from other types of detectors, such as photocells, IRdetectors, door switches, manually released signals and a possiblyexisting conventional alarm system.

The checking functions of the central unit:

Compare received signals with the data base to verify the authorizationof the chip.

Give an alarm in cases where data from chips do not correspond with thevalid states with which they are equipped.

Log the location of chips to be followed at any time.

Interpret signals from room detectors detecting movement in a zone, andsum up this against incoming data from chips in the zone. Give an alarmif unauthorized movement is registered.

Interpret data from other detectors (photocells etc.) and sum up thisagainst incoming data from chips in the zone. Give an alarm ifunauthorized movement is interpreted in the zone.

Catalogue information in the data base about chips which arecontinuously supervised.

The transmitters and receivers used in the chips, and possibly also inthe detectors, in the system according to the invention suitablycomprise electroacoustic transducers based on piezoelectric film ofpolyvinylidene fluoride (PVDF film). This technique is advantageous inthat it enables miniaturizing and economic manufacture of marker chipswhich are fit for placing on e.g. the back portion of patient journals.Such transducers can be used both in the audible frequency range and inthe ultrasonic range, and they can be used both as loudspeakers and asmicrophones in the sound-based data connection between the chips and thedetectors.

Acoustic radiation from a transducer requires volume excursion. As therelevant film thickness in this connection is of the order of 10 μm, thefilm will be too thin to achieve a sufficient volume excursion by meansof thickness variations of the film. Therefore, one must make use ofarea changes of the film. In order to transform area changes to volumechanges, the film must be curved in a preferably circular curve andclamped at opposite side edges of the film. By applying an alternatingvoltage to a pair of electrodes covering the two sides of the film,there is then achieved a pulsating movement transversely to the film.Because of the small thickness, the film will have a minimal bendingstiffness. Therefore, it must be prestressed with a mechanical springforce, fixed in a curved frame or be made self-supporting in thatseveral film layers are glued together. This applies both to soundtransmitters and to microphones.

For the applications of interest here, it may be advantageous to utilizetwo basic geometries, viz. 1) a piezo-electric film stretched over acurved supporting material, and 2) a self-supporting curved diaphragm.The first-mentioned design can be used both as a sound transmitter and amicrophone, whereas the latter is most suitable as a microphone.

Two embodiments of such electroacoustic transducers are schematicallyshown in FIGS. 5 and 6. Thus, FIG. 5 shows an embodiment of a transducer60 of the first-mentioned geometry, wherein a rectangular piece 61 of aPVDF film is stretched in the orientation direction over a flexiblesupporting material 62 which is circularly curved in cross-section andis fixed at the end edges 63, 64 where the associated line wires (notshown) are attached in a suitable manner, for example by glueing. Theflexible supporting material 62 is in turn supported by a rigid supportplate 65. The curvature of the film may vary and will be one of thefactors in optimalization with respect to sensitivity, frequencyresponse and linearity. The film suitably has a thickness of about 10μm, and the radius of curvature and angle of curvature of the film willbe optimized in dependence on the thickness and area of the film and therelevant operating frequency range.

Advantages of the embodiment according to FIG. 5 are that it has arelatively simple construction and is relatively robust, and that it maybe manufactured with a good sensitivity. Critical factors for theproperties of the transducer will be the quality of the supportingmaterial, and that a stable, resilient prestressing of the film isrequired.

A transducer embodiment according to the second basic geometry issuggested in FIG. 6. The figure shows a transducer 66 comprising a PVDFfilm which is shaped as a self-supporting diaphragm 67 which is fixed ina frame or a housing 68. The self-supporting diaphragm 67 is formed byjoining several layers of film. For a sound transmitter the thickness ofeach layer for considerations of sensitivity should not be thicker than5-10 μm. The sensitivity in principle is independent of the number oflayers. The layers must be connected in parallel, and in practice thismay be obtained by folding a film strip many times. Parallel connectiongives a low impedance (high capacitance).

For microphones the sensitivity is independent of the thickness of thefilm, and generally there may be used a film with such a thickness thatone layer will be self-supporting. If several layers are used, thesemust be connected in series. The internal impedance will be proportionalto the thickness.

Advantages of the embodiment according to FIG. 6 are that it has arelatively good sensitivity and is relatively robust, and further thatit is independent of supporting material, and therefore must be supposedto have a good long term stability.

Critical data for optimum sound pressure with a coverage angle of 120°for ultrasound and 180° for audio, are stated both for soundtransmitters and microphones in the table below.

Sound Sound transmit- transmit- Descrip- Microphone ter Microphone tertion ultrasound ultrasound audio audio Film 10 μm 10 μm 100 μm 10 μmthickness Angle of 20° 20° 60° 60° curvature Operating 25 kHz 25 kHz 5kHz 5 kHz frequency Area of 10 × 10 mm 10 × 10 mm 10 × 30 mm 10 × 30 mmfilm

As appears from the preceding description, the system according to theinvention combines two main functions:

1. An alarm system which is always active, but which fails to give analarm in case of authorized activity in the supervised area.

2. Automatic decision of location, identification and state ofelectronic marker chips placed on objects, in connection with e.g.service on equipment which is to be taken in for routinemaintenance/control. In the same manner the system may be used forlocalization, identification and authorization of persons, or when thechip ceases to send signals.

The main processes carried out by the present system are 1) Accesscontrol, 2) Object control and 3) Active message from ID chip. A surveyof functions and operations forming part of said main processes aregiven below.

Access Control

ID Chip (Marker Chip) in Normal Mode

US transmitter is passive.

US receiver listens continuously for commands from the room detectors.

The chip responds only to a call by transmitting its identification codevia the US or audio transmitter.

The ID chip possibly transmits command and identification if the chip isprogrammed to make itself known according to special criteria (Objectcontrol).

Room Detector in Normal State of Rest

US or audio receiver always listens.

US or sound transmitter is passive until the central gives a messageabout a call.

Detecting sensor is always active and forwards continuous messages tothe central about all movements in the room and cessation of signals.

Rom Detector in Detecting State

Detecting sensor detects movement in the room and sends a message to thecentral via the network that activity has been registered, and wherefromthe registration comes.

The central sends a message to the relevant room detector (and onlythis) to make a call via ultrasound or audio in the room and to ask thepresent ID chip to answer with its identification code.

The ID chip answers with its ID code.

The room detector receives the answer of the ID chip and transmits theanswer via the network to the central.

The central receives the answer and compares this with information aboutauthorized access. In case of unauthorized access an alarm is given. Incase of authorized access no reaction takes place.

The process goes on continuously at short time intervals as long asmovement is registered in the room, so that one or more new ID chips arechecked.

Object Control

Quiescent Mode

Room detector is in the same mode as for Access control.

The ID chip is normally passive and in listening mode.

Tracking of Object

The central transmits a general calling over the network to all roomdetectors, to call the ID chip or chips which is/are wanted.

All room detectors send out an ultrasonic or audio call in all rooms forthe desired ID chip of chips.

All ID chips listen for the call, but only the chip/chips recognizingits/their code, answers/answer.

The room detector receiving the answer, sends a message to the centralabout its registration, and the location or site of the ID chip therebyis known.

Active Message from ID Chip

An ID chip can be programmed to make itself known according topreprogrammed criteria. It may be time, number of registered incidentsor presences on a non-authorized location.

State of Rest

The ID chip is passive and only listens.

Active Calling from the ID Chip

The ID chip triggers itself to make itself known by transmitting itscode and a command to the nearest room detector with a message toforward a message to the central about its location.

The central sums up the automatic calling with stored information aboutthe chip and gives a message/alarm in accordance therewith.

Updating

The central calls chips in this category on a routine basis to checkthat they are present where they belong. If a chip answers from a placewhere it is not permitted to be, there may be given an alarm/message atthe central. If a chip does not respond to ultrasound, the chip will becalled by sound. It there is not given any answer on these callingsignals, an alarm may be given at the central.

Answer from ID Chip

It may occur that several ID chips are asked to answer simultaneously.Two chips which are transmitting at the same time, will disturb eachother and the signal will not be readable from any of these. To avoidthis problem, the chips emit their data pulse trains repeatedly atrandom intervals. The chips will then finally find a free time slotwherein the signal is alone and will be detected by the room detector.

Flowcharts illustrating operations carried out in the chips and in theroom detectors, are shown in FIGS. 7-9. Thus, the flowchart in FIG. 7shows operations carried out in a chip in the previously discussed,normal mode in which the US receiver listens continuously for commandsfrom the room detectors. FIG. 8 shows a corresponding flowchart to thatof FIG. 7, but also additional operations carried out in a chip providedwith an I/O unit 36 for transmission of operating data. Finally, theflowchart in FIG. 9 shows operating steps carried out in a room detectorin the detecting state.

What is claimed is:
 1. A system for supervision and control of objects or persons within a limited area, comprising a plurality of electronic identification chips for placing on respective objects/persons to be supervised/controlled, each chip having stored a special ID code and being provided with a transmitter and a receiver for communication via ultrasound, a plurality of stationary detectors interconnected in a network and arranged for both-way communication with the chips, and a central control unit communicating with the chips via the detectors, wherein each chip and each detector also is provided with a transmitter and a receiver for communication via audible sound (audio), a means being provided for switching between ultrasonic and audio communication, and that each chip in operation is continuously active and is arranged to transmit its ID code at predetermined time intervals, at least one of the detectors or the control unit being arranged to trigger an alarm unit if an incorrect code is received or an approved code is not received continuously at chosen time intervals.
 2. A system according to claim 1, wherein selected, special chips, are provided with a signal transmitter, which is arranged to deliver a signal in case of an alarm triggered by a neighboring detector.
 3. A system according to claim 1, wherein the chips are each programmed with a different gradation, the gradation specifying a larger or smaller part of said limited area to which the chip has access.
 4. A system according to claim 1, wherein each of the chips and the detectors contains a switching means in the form of a selector which is arranged to be controlled by a control circuit in the chip or detector in question, so that the selector provides for said switching at chosen time intervals.
 5. A system according to claim 1, wherein the transmitters and receivers in the chips comprise electroacoustic transducers in the form of a piezoelectric film of polyvinylidene fluoride (PVDF), wherein the film is mounted in a curved shape with a suitable angle of curvature which is optimized in dependence on the thickness and area of the film and the relevant operating frequency range.
 6. A system according to claim 5, wherein the PVDF film has a thickness of about 10 μm and is supported in a circular-cylindrically curved shape by a flexible supporting material which is supported by a rigid support plate.
 7. A system according to claim 5, wherein the PVDF film is formed as a self-supporting diaphragm.
 8. A system for supervision and control of objects or persons within a limited area, comprising a plurality of electronic identification chips for placing on respective objects/persons to be supervised/controlled, each chip having stored a special ID code and being provided with a transmitter and a receiver for communication via ultrasound, a plurality of stationary detectors interconnected in a network and arranged for both-way communication with the chips, and a central control unit communicating with the chips via the detectors, wherein each chip and each detector also is provided with a transmitter and a receiver for communication via audible sound (audio), a means being provided for switching between ultrasonic and audio communication, and that the central control unit is arranged to selectively call a selected chip via the detectors, and that the chips are arranged to give an answer as a reaction to the call, the closest situated detector then identifying the site/locality of the chip.
 9. A system according to claim 8, wherein the chips are arranged to activate themselves after a preprogrammed time interval, and then to transmit a message to the central control unit.
 10. A system according to claim 8, wherein at least one of the chips is provided with at least one input and at least one output for receiving and delivering information concerning service life or active operating time of respective objects on which the chips are mounted.
 11. A system according to claim 8, wherein each of the chips and the detectors contains a switching means in the form of a selector which is arranged to be controlled by a control circuit in the chip or detector in question, so that the selector provides for said switching at chosen time intervals.
 12. A system according to claim 8, wherein the transmitters and receivers in the chips comprise electroacoustic transducers in the form of a piezoelectric film of polyvinylidene fluoride (PVDF), wherein the film is mounted in a curved shape with a suitable angle of curvature which is optimized in dependence on the thickness and area of the film and the relevant operating frequency range.
 13. A system according to claim 12, wherein the PVDF film has a thickness of about 10 μm and is supported in a circular-cylindrically curved shape by a flexible supporting material which is supported by a rigid support plate.
 14. A system according to claim 12, wherein the PVDF film is formed as a self-supporting diaphragm. 